The present invention relates to a pay out system for paying out a flexible elongated element between two relatively movable objects, and also to a tension limiter device included in such a system.
The term "flexible elongated element" is used herein in a very broad sense, and is intended to include not only filaments, such as metal wires or optical fibers, but other types of devices, such as fluid-conducting tubes, radio-frequency waveguides, and the like, which may be payed out from one object moving relative to another object. The invention is particularly useful in a filament (e.g., metal wire or optical fiber) pay out system for an air vehicle launched from a launcher, and is therefore described below with respect to this application, but it will be appreciated that the invention could advantageously be used with respect to systems including other types of flexible elongated elements such as mentioned above.
Some types of air vehicles launched from a launcher are guided by a filament which is payed out as the air vehicle moves away from the launcher. The filament serves to feed the control commands to the air vehicle, and also to relay data sensed by the air vehicle back to the site of the launcher. The older systems used metal wire filaments for this purpose, but more recent systems use optical fiber filaments. In both cases the filaments are of very small diameter and therefore very light in weight, but nevertheless the filaments may be subjected to a substantial tension caused by wind drag as the filament is payed out because of the long length of the filament and the long time it is in the air. If the tension becomes excessive, the filament may break which would cause a catastrophic interruption in the communication with the air vehicle.